Palladium(II) acetate catalyzed reductive Heck reaction of enones: a practical approach

A surprisingly practical Pd(OAc)​2 or Pd(TFA)​2-​catalyzed reductive Heck reaction between aryl iodides and α,​β-​unsatd. ketones is described using N,​N-​diisopropylethylamine (DIPEA, Huenigs base) as the reductant. In general, 1 mol % of Pd(OAc)​2 is sufficient to afford good yields using electron-​rich or halogen-​substituted aryl iodides. Electron-​deficient aryl iodides preferentially give homocoupling. Enones contg. aryl or bulky substituents on the β-​carbon react smoothly, producing mainly reductive Heck product, whereas enones with alkyl substituents on the β-​carbon afford a mixt. of reductive Heck and Heck product. Deuterium labeling expts. show that the reaction is a bona fide reductive Heck reaction and exclude a Heck reaction-​conjugate redn. cascade.